A substrate processing apparatus is used to perform certain processes such as an etching process or a film forming process on a substrate to be processed such as a glass substrate (e.g., a liquid crystal substrate) or a semiconductor wafer (hereinafter, simply referred to as a “wafer”). The substrate processing apparatus includes, e.g., a processing unit containing a processing chamber for performing a certain process on a wafer, and a load-lock chamber connected to the processing chamber. The substrate processing apparatus further includes a cassette stage, on which a cassette container is placed, the cassette container accommodating an unprocessed wafer to be loaded into the apparatus or a processed wafer to be unloaded from the apparatus, a lid detachment mechanism for attaching/detaching a lid to/from the cassette container (see, e.g., Japanese Patent Laid-open Publication No. H10-125763), and a transfer chamber provided with a transfer mechanism, such as a transfer arm, to perform wafer delivery between the cassette container and the processing unit.
In the substrate processing apparatus, when the cassette container accommodating an unprocessed wafer is placed on the cassette stage, the lid is detached from the cassette container by using the lid detachment mechanism. Thereafter, the unprocessed wafer is unloaded from the cassette container by using the transfer mechanism provided in the transfer chamber, and then delivered to the processing unit. The unprocessed wafer is transferred to the processing chamber via the load-lock chamber. A certain process is carried out on the wafer in the processing chamber. The wafer completely processed in the processing chamber is returned from the processing chamber to the load-lock chamber. The transfer mechanism provided in the transfer chamber receives the processed wafer returned to the load-lock chamber, and transfers the processed wafer to the cassette container.
In the transfer chamber, transfer of an unprocessed wafer or a processed wafer is performed by using the transfer mechanism, as mentioned above. Accordingly, particles (e.g., dust, dirt, deposit, and reaction products) float in the transfer chamber due to operations carried out in the transfer chamber, e.g., wafer transferring operations. As a result, particles may be adhered to a surface of a wafer during transfer of the wafer. When a process is performed on the wafer with particles adhered, degradation in yield may occur. For example, in an etching process, the particles adhered to the surface of the wafer may function as a mask, thereby generating etching residues. Further, in a film forming process, the particles adhered to the surface of the wafer may function as nuclei, so that they may cause degradation in film quality due to growth thereof. Thus, generally, a nonreactive gas such as N2 gas or clean air is supplied to the transfer chamber via a high efficiency particulate air (HEPA) filter or an ultra low penetration air (ULPA) filter.
However, it may be impossible to completely remove contaminants only by supplying, e.g., clean air to the transfer chamber via the HEPA filter or ULPA filter. For example, substances, which may remain floating in the transfer chamber without being completely removed, include molecules of a lubricant such as grease used in a driving system including the transfer mechanism and the lid detachment mechanism, water molecules, impure gas molecules such as ammonia, organic matter produced from line materials adhered to the processed wafer (see, e.g., Japanese Patent Laid-open Publication No. 2003-7799).
Accordingly, attempts have been continuously made to reduce the amount of contaminants in the transfer chamber by providing a chemical filter using activated carbon instead of the HEPA filter or ULPA filter, or to suppress the generation of particles in the transfer chamber through selection of parts or adjustment of devices.
Meanwhile, in the above-mentioned substrate processing apparatus, the wafer accommodated in the cassette container is transferred, for processing thereof, to the processing chamber via at least one chamber, that is, the transfer chamber or the load-lock chamber.
Further, in a so-called cluster tool type substrate processing apparatus including processing units, a plurality of processing chambers are connected to a common transfer chamber. The common transfer chamber is connected to the transfer chamber via a load-lock chamber. In such a substrate processing apparatus, the wafer accommodated in the cassette container is transferred, for processing thereof, to the processing chamber via, e.g., the above-mentioned transfer chamber, the load-lock chamber and the common transfer chamber.
Thus, the wafer may be affected by particles not only in the transfer chamber, but also in other chambers, until it is processed after being transferred from the cassette container to the processing chamber. Accordingly, various techniques have been proposed to prevent generation of particles in each chamber. For example, Japanese Patent Laid-open Publication No. H9-82781 discloses a technique for preventing reaction by-products from being adhered to respective inner walls of a reaction chamber (processing chamber) and a transfer chamber by adjusting the internal temperatures of the reaction chamber and the transfer chamber. In accordance with this technique, it is possible to suppress generation of particles caused by reaction by-products, the particles being possibly adhered to the inner walls of the reaction chamber and transfer chamber.
In spite of the above-mentioned countermeasure, however, it is very difficult to completely remove particles from each chamber of the semiconductor processing apparatus. Recently, the design rule of semiconductor integrated circuits has been gradually reduced. Accordingly, there has been a demand for a technique for preventing an even very small amount of particles from being adhered to the surface of a wafer in a stage before the wafer is processed in the processing chamber (a stage until the wafer is completely transferred, for the processing thereof, from the cassette container to the processing chamber). That is, the technique for preventing particles from being adhered to the surface of a wafer in each chamber, in order to transfer a clean wafer, to which no particles are adhered, to the processing chamber, has also been highlighted, in addition to the technique for reducing the amount of particles in each chamber.
Also, Japanese Patent Laid-open Publication No. 2005-354025 discloses a method for peeling off particles adhered to the surface of a wafer loaded in a wafer loading part of a transfer arm by establishing a certain temperature gradient in the wafer loading part, to remove the particles. In accordance with this method, it may be possible to remove particles from a wafer while the wafer is loaded in the wafer loading part of the transfer arm. Thus, an enhancement in throughput may be achieved.
However, the technique disclosed in Japanese Patent Laid-open Publication No. 2005-354025 is different from the technique for preventing particles from being adhered to the surface of the wafer in that the disclosed technique removes particles adhered to the wafer by peeling off the particles. As disclosed in the Patent Document, a certain amount of energy is needed to effectively remove the particles adhered to the wafer through a peel-off method. Accordingly, it is necessary to set the temperature applied to the wafer loading part to a relatively high level (e.g., a level higher than the temperature of the processing chamber by 30K or more). However, it is desirable to avoid application of high-temperature heat to the wafer, if at all possible, in terms of the maintenance of a desired wafer quality and the saving of energy. Further, it may be impossible to completely remove particles, even by using the above-mentioned technique, because particles having a smaller size exhibit higher adherence.
From the above description, it is necessary to provide a technique capable of preventing particles from being adhered to the surface of a wafer without causing the wafer to be heated to high temperature, and thus transferring the wafer in a clean state to the processing chamber, in which a desired process is performed on the wafer.